The RTK (Real Time kinematic) system is a positioning method for determining the three-dimensional position of a measurement object (hereinafter, will be called a measuring point) in real time by means of GPS (Global Positioning System). The RTK system is also used for tsunami/ocean wave observation using marine research buoys.
In the RTK system, a carrier phase at a measuring point is measured with reference to the measured value of a carrier phase at a reference point from a GPS satellite. The latitude, longitude, and height of the reference point have been determined beforehand. Further, a baseline vector is determined when the measuring point is viewed from the reference point, and the three-dimensional position of the measuring point is precisely measured. In the RTK system, an integer bias for the measured value of the carrier phase is determined, achieving high-precision positioning.
However, for example, when sea level positions, that is, sea level displacements are successively measured in the RTK system, an integer bias may be erroneously determined because of the influence of the ionosphere and the troposphere or factors such as a cycle slip of a GPS receiver, resulting in a jumping phenomenon of rapidly changing GPS ranging data (data corresponding to a distance between a GPS satellite and a receiver). This phenomenon may reduce the reliability of the GPS ranging data and cause a false warning in, e.g., tsunami observation.
In order to solve this problem, a technique is currently available for the identification of GPS positioning data (three-dimensional position data computed based on a GPS satellite position and GPS ranging data) erroneously recognized by a jumping phenomenon, based on information about whether a current solution is a fix solution or a less accurate solution (e.g., see Japanese Patent Laid-Open No. 2008-2975).